> Why does the data for a CDS need to be on a doubleword anyway? "It just does" Or if you want the more gory explanation... it has to do with storage operand consistency rules. CDS is built on top of the hardware memory architecture and so it has to play within the same rules as other storage access operations. The hardware guarantees consistent (i.e. the same to all observers) block concurrent access to the contents of a doubleword but if you cross a doubleword boundary you are by definitiion accessing two different double words and you lose the consistency guarantee. Read about it in Principles of Operation.
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